How Can I Specify a Cross-Platform DLL Import Path at Runtime in C#?

Specify cross-platform DLL import path when running in C#

When integrating external C DLLs in a C# project, it can be challenging to go beyond statically defined values ​​to customize the DLL's import path. This article addresses this issue, focusing specifically on specifying import paths at runtime.

While using the DllImport attribute is still the preferred method, it requires the DLL directory to use constant string parameters, which is a limitation. This rigidity can be a hindrance in situations where the DLL location may vary between different user environments.

Solution using relative path

Contrary to popular belief, DllImport properties are still available. Rather than relying on absolute paths, specifying the relative path to the DLL will solve the problem. The default search order for DLLs includes the application's directory, ensuring that the DLL is found during installation.

Use SetDllDirectory

If relative paths don’t work, or you need to dynamically customize the path, you can use the SetDllDirectory function. Calling this function before accessing imported DLL functions allows the default DLL search path to be modified.

P/Invoke statement of SetDllDirectory

To use SetDllDirectory, perform the following P/Invoke import:

[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
static extern bool SetDllDirectory(string lpPathName);

The DLL search path can be adjusted at runtime by dynamically setting the lpPathName parameter.

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